Change default plan

Right now, the default plan on the register page is the first paid plan that I have. I want to make it so that the free plan is selected. The logic for this isn't in a component file, it's in mixins/register.js, so it can't be overridden using the method described in the docs.

I tried adding code to re-select the free plan in resources/assets/js/spark-components/auth/register-stripe.js, but this executes before the plan selection logic as it retrieves the plan list via ajax first.